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1.
    
  1. Climate change is already having profound impacts upon the state and dynamics of lake ecosystems globally. A specific concern is that climate change will continue to promote the growth of phytoplankton, particularly blooms of toxic cyanobacteria, via lake physical processes including warming surface waters and shallowing of the mixed layer. These two mechanisms will have different impacts on lake phytoplankton communities, but their inter‐connectedness has made it difficult to disentangle their independent effects.
  2. We fill this knowledge gap by performing 1666 numerical modelling experiments with the phytoplankton community model, PROTECH, in which we separated the independent effects on lake phytoplankton of temperature change and changes in the depth of the surface mixed layer. Given the large global abundance of small lakes (<1 km2) and the importance of their ecosystems in global processes and budgets, we used a small meso‐eutrophic lake as an example study site for the modelling experiments.
  3. Increasing the lake temperature and positioning the mixed layer at a shallower depth had different ecological impacts, with warming typically resulting in more biomass and a dominance of cyanobacteria.
  4. The response to mixed depth shallowing depended on the original depth where mixing occurred. As anticipated, where the original mixed depth was moderate (4–6 m) and there was a simultaneous increase in water temperature, cyanobacterial biomass increased. However, when the same absolute difference in shallowing and temperature increase were applied to a deeper mixed depth (9–13 m), lower cyanobacterial biomass resulted, owing to poorer conditions for low‐light tolerant cyanobacteria.
  5. Our study shows that the response of cyanobacterial blooms to climate‐induced warming and shallowing of mixed layers in lakes around the world will not be universal, but rather will be system‐specific, depending upon the average mixed layer depth of the lake in question and the light affinity of the dominant cyanobacteria species.
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2.
The phytoplankton lake community model PROTECH (Phytoplankton RespOnses To Environmental CHange) was applied to the eutrophic lake, Esthwaite Water (United Kingdom). It was validated against monitoring data from 2003 and simulated well the seasonal pattern of total chlorophyll, diatom chlorophyll and Cyanobacteria chlorophyll with respective R2‐values calculated between observed and simulated of 0.68, 0.72 and 0.77 (all P<0.01). This simulation was then rerun through various combinations of factorized changes covering a range of half to double the flushing rate and from ?1 to +4 °C changes in water temperature. Their effect on the phytoplankton was measured as annual, spring, summer and autumn means of the total and species chlorophyll concentrations. In addition, Cyanobacteria mean percentage abundance (%Cb) and maximum percentage abundance (Max %Cb) was recorded, as were the number of days that Cyanobacteria chlorophyll concentration exceed two World Health Organization (WHO) derived risk thresholds (10 and 50 mg m?3). The phytoplankton community was dominated in the year by three of the eight phytoplankton simulated. The vernal bloom of the diatom Asterionella showed little annual or seasonal response to the changing drivers but this was not the case for the two Cyanobacteria that also dominated, Anabaena and Aphanizomenon . These Cyanobacteria showed enhanced abundance, community dominance and increased duration above the highest WHO risk threshold with increasing water temperature and decreasing flushing rate: this effect was greatest in the summer period. However, the response was ultimately controlled by the availability of nutrients, particularly phosphorus and nitrogen, with occasional declines in the latter's concentration helping the dominance of these nitrogen‐fixing phytoplankton.  相似文献   

3.
    
Lough Neagh is the largest lake in the UK and has been extensively monitored since 1974. It has suffered from considerable eutrophication and toxic algal blooms. The lake continues to endure many of the symptoms of nutrient enrichment despite improvements in nutrient management throughout the catchment, in particular a permanently dominant crop of the cyanobacterium Planktothrix agardhii. This study examines the historical changes in the Lough, and uses the PROTECH lake model to predict how the phytoplankton community may adapt in response to potential future changes in air temperature and nutrient load. PROTECH was calibrated against 2008 observations, with a restriction on the maximum simulated mixed depth to reflect the shallow nature of the lake and the addition of sediment released phosphorus throughout the mixed water column between 1 May and 1 October (with an equivalent in-lake concentration of 2.0 mg m−3). The historical analysis showed that phytoplankton biomass (total chlorophyll a) experienced a steady decline since the mid-1990s. During the same period the key nutrients for phytoplankton growth in the lake have shown contrasting trends, with increases in phosphorus concentrations and declines in nitrate concentrations. The modelled future scenarios which simulated a temperature increase of up to 3 °C showed a continuation of those trends, i.e. total chlorophyll a and nitrate concentrations declined in the surface water, while phosphorus concentrations increased and P. agardhii dominated. However, scenarios which simulated a 4 °C increase in air temperature showed a switch in dominance to the cyanobacteria, Dolichospermum spp. (formerly Anabaena spp.). This change was caused by a temperature related increase in growth driving nutrient consumption to a point where nitrate was limiting, allowing the nitrogen-fixing Dolichospermum spp. to gain sufficient advantage. These results suggest that in the long term, one nuisance cyanobacteria bloom may only be replaced by another unless the in-lake phosphorus concentration can be greatly reduced.  相似文献   

4.
In this article, we show by mesocosm experiments that winter and spring warming will lead to substantial changes in the spring bloom of phytoplankton. The timing of the spring bloom shows only little response to warming as such, while light appears to play a more important role in its initiation. The daily light dose needed for the start of the phytoplankton spring bloom in our experiments agrees well with a recently published critical light intensity found in a field survey of the North Atlantic (around 1.3 mol photons m?2 day?1). Experimental temperature elevation had a strong effect on phytoplankton peak biomass (decreasing with temperature), mean cell size (decreasing with temperature) and on the share of microplankton diatoms (decreasing with temperature). All these changes will lead to poorer feeding conditions for copepod zooplankton and, thus, to a less efficient energy transfer from primary to fish production under a warmer climate.  相似文献   

5.
    
Many shallow lakes in north temperate zones experience reduced dissolved oxygen concentration under ice. However, some shallow lakes display supersaturated dissolved oxygen concentrations (>20 mg·L ? 1) in late winter under conditions of maximum ice thickness. During the winters of 1996, 1997, and 1999, we collected phytoplankton samples from Arrowwood Lake near Pingree, North Dakota to determine whether a specific alga was involved in dissolved oxygen supersaturation in this lake. Although dissolved oxygen supersaturation was not observed during this period, we did observe an increase in dissolved oxygen concentration that was associated with a phytoplankton bloom during late February and early March in both 1996 and 1997. In 1996, the bloom was composed of the dinoflagellate, Peridinium aciculiferum (Lemm.) Lemm. and several species of cryptomonads. A similar bloom of P. aciculiferum was followed by a bloom of several species of euglenoids in 1997. In contrast, P. aciculiferum was only a minor component of the winter phytoplankton, dissolved oxygen concentrations remained low, and no bloom event was observed in 1999. Statistical analyses indicated a significant relationship (rs = 0.57, P = 0.019) between dissolved oxygen levels and the density of the dinoflagellate, P. aciculiferum, but no significant relationship between dissolved oxygen levels and densities of other phytoplankton. These results suggest that the elevated levels of dissolved oxygen are associated with the dinoflagellate, P. aciculiferum. This bloom was most likely the result of an excystment event rather than a general growth response.  相似文献   

6.
    
  1. Periods of hypoxia lasting up to weeks are now anticipated in fresh waters, owing to anthropogenic influences. However, the cumulative effects of hypoxia on Daphnia, over multiple broods, have received virtually no attention, and to establish and evaluate such responses there is a need to make measurements over a wide range of oxygen concentrations, potentially revealing non‐linear patterns. We predict that the effect of hypoxia on growth, survival and fecundity (i.e., production of new individuals) of Daphnia will increase over multiple broods, and with increasing oxygen these responses will approach asymptotic maxima, following a rectangular hyperbolic response.
  2. Daphnia similoides were exposed to 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 and 8.0 mg oxygen L?1. To determine effects on the first brood we examined: number of offspring; time to the first eggs; time to the first brood and size of the female at the first eggs and the first brood. To determine cumulative effects of oxygen over multiple broods (up to 8 broods over 21 days), we measured: total number of offspring produced by a female; survival time and total number of moults and broods. To investigate how the cumulative effects arose over the multiple broods, we examined the number of offspring per brood in each brood over eight broods. To assess treatment effects and indicate responses, functions were fit to data using the most parsimonious function that reflected trends in the data.
  3. Measurements associated with a single brood responded linearly, or not at all, with changing oxygen concentration, whereas measurements made over the 21 days followed a rectangular hyperbolic response, increasing to an asymptote as oxygen increased. For the first brood, as oxygen concentration was raised from 1 to 8 mg L?1 the number of offspring produced and the time required to produce the brood were not affected; the time required to produce eggs decreased ?0.3‐fold; and the size of individuals at the time when the eggs and the brood were produced increased ?0.1‐fold. Over the 21 days, between 1 and 8 mg L?1 the total number of offspring increased ?3.4‐fold; individual survival and the number of moults increased ?2‐fold, and the number of broods increased ?1‐fold. For single‐brood responses, there was no effect of decreasing oxygen levels on the number of offspring in the first brood, but there were negative effects on the second‐to‐fourth broods; the number of offspring in the remaining broods was not significantly related to oxygen levels, as there were fewer data at low levels due to poor survival.
  4. We conclude that assessments of Daphnia demographics should not rely on estimates of the effect of oxygen concentration on single broods. Instead, studies should consider cumulative changes over multiple broods. Following our approach, researchers may now explore the impacts of hypoxia on congeners and other zooplankton, and investigate the mechanisms associated with multi‐brood responses.
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7.
    
  1. Harmful cyanobacterial blooms are an increasing problem at many locations throughout the world but are rarely reported in aquatic habitats at high latitudes. Shallow lakes are a major feature of northern permafrost landscapes and are likely to experience large‐scale changes in their limnological properties in the future as a consequence of climate warming.
  2. In the present study, we addressed the question of what preconditions would be necessary to stimulate the growth and dominance of bloom‐forming cyanobacteria in northern fresh waters. We analysed the summer phytoplankton of 18 lakes on eroding permafrost (thaw lakes) and on glacier‐scoured rock (rock basin lakes) in subarctic Quebec, Canada, to determine their phytoplankton community structure and the biomass contribution of cyanobacteria. This survey was complemented with an incubation experiment to evaluate the direct warming and indirect phosphorus (P) enrichment effects of climate change on cyanobacterial bloom development.
  3. All lakes contained diverse phytoplankton communities, often dominated by chrysophytes, dinoflagellates and chlorophytes. Cyanobacteria were present in all waterbodies, but their contribution to the total community biovolume was highly variable (mean of 8.7%, range 0.1%–47%). Cyanobacterial community biovolumes correlated positively with surface water temperatures, and negatively with dissolved organic carbon, soluble reactive phosphorus, iron and manganese concentrations in the surface waters.
  4. Phosphorus enrichment of water from a thaw lake resulted in a fourfold increase of chlorophyll a (Chl‐a) and an increase in the cyanobacterial pigments echinenone and zeaxanthin. The phytoplankton counts showed that there was a sharp decrease in diversity (expressed as decline of the Shannon–Wiener index from 1.69 to 0.16), accompanied by a shift to cyanobacterial dominance, notably by the heterocystous, potentially toxic species Dolichospermum cf. planctonicum. Increased temperature led to an initial doubling of cyanobacterial biovolume, followed by the development of a chrysophyte bloom. Combined warming and P enrichment led to reduced phytoplankton biodiversity, with a community composed of cyanobacteria and chrysophytes. There was also a pronounced response by the picophytoplankton community; picocyanobacteria were strongly stimulated by P enrichment, while picoeukaryotes increased in response to warming.
  5. The current inoculum levels of cyanobacteria in subarctic lakes and their responsiveness to temperature and phosphorus indicate the potential for an abrupt increase in their abundance, accompanied by a decrease in phytoplankton diversity. Ongoing climate change will increase the risk of noxious cyanobacterial blooms in northern lakes and ponds, with potentially negative consequences for higher trophic levels.
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8.
    
  1. The high Arctic, including the Svalbard archipelago in the North Atlantic, has been exposed to direct and indirect drivers of climatic change such as rising temperatures and associated changes in hydrology and nutrient fluxes. In addition, the number of migrating birds, particularly geese, increased remarkably in the Svalbard archipelago during the second half of the last century. The higher number of breeding birds potentially affects water quality and the biota in ponds and lakes.
  2. We aimed to investigate the potential influence of increasing goose abundance on trophic state, taxon richness, and species composition of freshwater communities in the high Arctic. We hypothesised that higher goose abundance affects the trophic state of shallow lakes and ponds and their taxon richness and species composition. We conducted a survey of selected ponds at Svalbard along a goose abundance gradient. We used the number of area‐specific goose droppings (range of 0–94 droppings m2) as a proxy of goose presence and measured proxies for productivity as well as taxon richness and composition of phytoplankton and invertebrate communities.
  3. Presence and abundance of geese were associated with higher productivity of ponds. Invertebrate and phytoplankton taxon richness correlated (positively) with goose abundance. Both phytoplankton and invertebrate taxon richness increased with increasing nitrogen (N) concentrations. Goose abundance significantly affected phytoplankton species composition, while concentrations of total‐N and total phosphorus (P) did not. Species composition of aquatic invertebrates was most strongly affected by goose abundance, but the effect of total‐N concentration was also significant.
  4. Increased goose abundance was associated with bird driven nutrient enrichment, increased phytoplankton and invertebrate taxon richness and changes of these biological communities. Thus, in addition to climate change, the higher abundances of large migratory water fowl in many polar areas may pose a major additional stress to arctic lakes and ponds. In fact, climate change and bird impact may interact, accelerating ongoing environmental change of arctic freshwater ecosystems.
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9.
    
  1. Globally, freshwater ecosystems are warming at unprecedented rates and northern temperate lakes are simultaneously experiencing increased runoff of humic substances (brownification), with little known consequences for future conservation of biodiversity and ecosystem functioning.
  2. We employed an outdoor mesocosm experiment during spring and summer to investigate the combined effects of gradually increasing warming and brownification perturbations on the phytoplankton community structure (biodiversity and composition) and functioning (biomass).
  3. While we did not observe overall significant treatment effects on total phytoplankton biomasses, we show that predicted increases in warming and brownification can reduce biodiversity considerably, occasionally up to 90% of Shannon diversity estimates. Our results demonstrate that the loss of biodiversity is driven by the dominance of mixotrophic algae (Dinobryon and Cryptomonas), whereas several other phytoplankton taxa may be temporarily displaced from the community, including Cyclotella, Desmodesmus, Monoraphidium, Tetraedron, Nitzschia and Golenkinia.
  4. The observed loss of biodiversity coincided with an increase in bacterial production providing resources for potential mixotrophs along the gradient of warming and brownification. This coupling between bacterial production and mixotrophs was likely a major cause behind the competitive displacement of obligate phototrophs and supports evidence for the importance of consumer–prey dynamics in shaping environmental impacts on phytoplankton communities.
  5. We conclude that warming and brownification are likely to cause a profound loss of biodiversity by indirectly affecting competitive interactions among phytoplankton taxa. Importantly, our results did not show an abrupt loss of biodiversity; instead the reduction in taxa richness levelled off after exceeding a threshold of warming and brownification. These results exemplify the complex nonlinear responses of biodiversity to environmental perturbations and provide further insights for predicting biodiversity patterns to the future warming and brownification of freshwaters.
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10.
  总被引：1，自引：0，他引：1  
  1. We tested the hypothesis that higher temperature and dissolved organic carbon (DOC) concentration increase dissolved and particulate carbon (C) relative to phosphorus (P), thereby reducing algal food quality for P‐limited cladocerans while not affecting N‐limited copepods. Also, we expected alpine zooplankton to respond more strongly than those from warmer montane lakes to increased water temperature.
  2. Plankton from two alpine lakes and two montane lakes were incubated in vitro for 30 days at 10 or 17 °C and with ambient or +80% DOC, which was achieved by concentrating humic substances from each lake via reverse osmosis.
  3. Dissolved organic carbon amendments and warming significantly increase particulate C : P under montane, but not alpine conditions. While higher water temperature and DOC separately reduced phytoplankton abundance, together they increased phytoplankton by stimulating uptake of P. Warming stimulated only Daphnia while suppressing the abundance of the calanoid copepod Hesperodiaptomus when they originated from the three coldest lakes. Particulate C : P was positively correlated with Daphnia abundance and negatively correlated with Hesperodiaptomus, probably due to greater P‐retention by Daphnia.
  4. Our findings highlight the importance of interactions between the ecological effects of higher temperature and increased inputs of terrestrial organic matter to forecasts of the net impact of global warming on mountain lakes. Such predictions may be confounded if they are derived solely from the expected sum of single effects by each climatic factor.
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11.
    
Climate warming alters the seasonal timing of biological events. This raises concerns that species-specific responses to warming may de-synchronize co-evolved consumer-resource phenologies, resulting in trophic mismatch and altered ecosystem dynamics. We explored the effects of warming on the synchrony of two events: the onset of the phytoplankton spring bloom and the spring/summer maximum of the grazer Daphnia. Simulation of 16 lake types over 31 years at 1907 North African and European locations under 5 climate scenarios revealed that the current median phenological delay between the two events varies greatly (20–190 days) across lake types and geographic locations. Warming moves both events forward in time and can lengthen or shorten the delay between them by up to ±60 days. Our simulations suggest large geographic and lake-specific variations in phenological synchrony, provide quantitative predictions of its dependence on physical lake properties and geographic location and highlight research needs concerning its ecological consequences.  相似文献   

12.
Indoor mesocosms were used to study the combined effect of warming and of different densities of overwintering mesozooplankton (mainly copepods) on the spring development of phytoplankton in shallow, coastal waters. Similar to previous studies, warming accelerated the spring phytoplankton peak by ca. 1 day °C?1 whereas zooplankton did not significantly influence timing. Phytoplankton biomass during the experimental period decreased with warming and with higher densities of overwintering zooplankton. Similarly, average cell size and average effective particle size (here: colony size) decreased both with zooplankton density and warming. A decrease in phytoplankton particle size is generally considered at typical footprint of copepod grazing. We conclude that warming induced changes in the magnitude and structure of the phytoplankton spring bloom cannot be understood without considering grazing by overwintering zooplankton.  相似文献   

13.
    
  1. Studies examining the consequences of increased partial pressure of carbon dioxide (pCO2) in freshwater ecosystems associated with climate change have focused on direct effects for phytoplankton, showing increases in primary productivity, biomass or altered composition. However, in lakes, phytoplankton dynamics are also regulated by zooplankton predation and thermal stratification which can lead to a concentration of phytoplankton biomass in a deep chlorophyll maximum (DCM) layer, making the response to CO2 increase important to understand here.
  2. Mesocosm experiments were conducted in a meso‐oligotrophic north temperate lake with a strong summer phytoplankton DCM, to estimate the independent and interaction effects of zooplankton grazing and elevated pCO2 on water column phytoplankton communities and on DCM characteristics.
  3. Interaction of CO2 effects with zooplankton grazing occurred for three of four phytoplankton spectral groups, influencing water column phytoplankton biomass. Zooplankton selective grazing appeared as important as CO2 concentration in controlling phytoplankton population and biomass. Unexpectedly, CO2 had an overall negative effect on phytoplankton total biomass despite positive productivity responses.
  4. Elevated CO2 led to more peaked (stronger vertical gradient) mid‐water column chlorophyll distribution, but to smaller DCM peaks overall. Zooplankton had unexpected effects, inducing clustering of more edible phytoplankton and greater temporal variation in the DCM.
  5. Our experiment points to interactions in the microbial food web and stoichiometric considerations with nutrient addition that should be explored further in future work with realistic lake food webs to better understand these complex responses to CO2.
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14.
T. Frisk 《Hydrobiologia》1982,86(1-2):133-139
A simple water quality model for Lake Haukivesi, heavily loaded by pulp and paper mill effluents, has been developed. The main purpose of the model is to predict the concentration of dissolved oxygen in the hypolimnion. The lake is divided into seven sub-basins, and also into epilimnion and hypolimnion. Transfers between sub-basins are calculated using water balance equations. The state variables of the model are dissolved oxygen concentration, biochemical oxygen demand, phytoplankton biomass, and total phosphorus concentration. The effect of temperature on reaction rate coefficients has been taken into account. Temperature is calculated in the model using a second degree polynomial function. The processes affecting hypolimnetic oxygen consumption are BOD decay, decomposition of phytoplankton, benthic oxygen demand, and decomposition of slowly decaying organic matter.  相似文献   

15.
    
  1. Atmospheric changes are leading to the browning of northern lakes (i.e. increases in catchment‐derived dissolved organic matter [DOM]), consequently altering phytoplankton biomass and community composition.
  2. We hypothesised that lake browning and the concurrent increase in nutrients drive a shift towards greater cyanobacteria biomass. We further hypothesised that, as a consequence of this shift in phytoplankton, the content of ω‐3 (n‐3) essential fatty acids (EFA) in seston would decline, affecting the subsequent transfer of EFA to consumers across the plant–animal interface in pelagic regions of lakes.
  3. We tested these hypotheses in the epilimnion of 30 temperate lakes in Ontario (Canada), representing a gradient of lake browning, with dissolved organic carbon (DOC) ranging from 2 to 10 mg/L and total phosphorus ranging from 6.0 to 48.5 μg/L. In each of these lakes, the concentration and composition of DOM, the biomass of phytoplankton and cyanobacteria, and the EFA content of seston, cladocerans, and copepods were measured.
  4. An increase in aromatic DOM was associated with increased phytoplankton and cyanobacteria biomass. Due to the lower content of the EFA eicosapentaenoic acid (EPA; 20:5n‐3) and docosahexaenoic acid (DHA; 22:6n‐3) in cyanobacteria, this increase in phytoplankton biomass was associated with a decline in EPA and DHA content in lake seston. However, there was no significant change in EFA content of cladocerans and copepods. This homeostatic (diet‐independent) EFA composition in zooplankton suggested that, as the phytoplankton community shifted towards more cyanobacteria with lower EFA content, the cladocerans and copepods may have met their nutritional requirements by relying on alternative food sources (e.g. heterotrophic ciliates and flagellates) capable of either trophically upgrading phytoplankton‐produced EPA and DHA, or synthesising EPA and DHA de novo.
  5. Results from this study indicate that increasing DOC from low (2 mg DOC/L) to moderate levels (15 mg DOC/L) may increase the importance of the microbial pathway in the trophic transfer of EPA and DHA from basal resources to zooplankton. However, this supplementary transfer of EFA through the microbial food web may not sustain high EPA and DHA levels in zooplankton when lake browning starts to limit primary production (>15 mg DOC/L).
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16.
Although the consequences of global warming in aquatic ecosystems are only beginning to be revealed, a key to forecasting the impact on aquatic communities is an understanding of individual species' vulnerability to increased temperature. Despite their microscopic size, phytoplankton support about half of the global primary production, drive essential biogeochemical cycles and represent the basis of the aquatic food web. At present, it is known that phytoplankton are important targets and, consequently, harbingers of climate change in aquatic systems. Therefore, investigating the capacity of phytoplankton to adapt to the predicted warming has become a relevant issue. However, considering the polyphyletic complexity of the phytoplankton community, different responses to increased temperature are expected. We experimentally tested the effects of warming on 12 species of phytoplankton isolated from a variety of environments by using a mechanistic approach able to assess evolutionary adaptation (the so-called ratchet technique). We found different degrees of tolerance to temperature rises and an interspecific capacity for genetic adaptation. The thermal resistance level reached by each species is discussed in relation to their respective original habitats. Our study additionally provides evidence on the most resistant phytoplankton groups in a future warming scenario.  相似文献   

17.
    
  1. In our recent contribution to the special issue on plankton dynamics in a fast‐changing world, we outlined some general predictions of plankton dynamics in different climate regions now and in future, building on the Plankton Ecology Group (PEG) model (de Senerpont Domis et al., 2013).
  2. We proposed a stylised version of plankton dynamics in Fig. 3 of our article and stated that these patterns need to be further elaborated. Our figure displays annual plankton dynamics now and in future in oligotrophic, mesotrophic and eutrophic lakes in arctic, temperate and tropical climate zones.
  3. We fully agree with Sarmento, Amado & Descy (2013) that more data on tropical regions are needed, and we are looking forward to the emergence of published data from tropical regions to extend our still‐limited understanding of plankton dynamics in these regions.
  4. Sarmento et al. (2013) did not agree with our predictions on plankton dynamics for hydrology‐driven water systems in the tropics. Unfortunately, however, Sarmento et al. (2013) did not substantiate their statements with the much‐needed data on plankton dynamics in the tropics. Moreover, they merely provide an overview of precipitation patterns in the tropics, not an alternative hypothesis for our predictions.
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18.
    
Ecosystem processes vary temporally due to environmental fluctuations, such as when variation in solar energy causes diurnal cycles in primary production. This normal variation in ecosystem functioning may be disrupted and even lost if taxa contributing to functioning go extinct due to environmental stress. However, when communities are exposed to the stress at sub-lethal levels over several generations, they may be able to develop community-level stress tolerance via ecological (e.g. species sorting) or evolutionary (e.g. selection for tolerant genotypes) mechanisms and thus avoid the loss of stability, as defined by the resistance of a process. Community tolerance to a novel stressor is expected to increase the resistance of key processes in stressed ecosystems. In freshwater communities we tested whether prolonged prior exposure to an environmental stressor, i.e. acidification, could increase ecosystem stability when the communities were exposed to a subsequent press perturbation of more severe acidification. As a measure of ecosystem stability, we quantified the diurnal variation in dissolved oxygen (DO), and the resistance of the DO cycle and phytoplankton biomass. High-frequency data from oxygen loggers deployed in 12 mesocosms showed that severe acidification with sulfuric acid to pH 3 could cause a temporary (i.e. two-week long) loss of diurnal variation in dissolved oxygen concentration. The loss of diurnal variation was accompanied by a strong reduction in phytoplankton biomass. However, the pre-exposure to acidification for several weeks resulted in the maintenance of the diurnal cycle and higher levels of phytoplankton biomass, though they did not return to as rapidly to pre-exposure functioning as non-exposed mesocosms. These results suggest that ecosystem stability is intrinsically linked to community-wide stress tolerance, and that a history of exposure to the stressor may increase resistance to it, though at the cost of some resilience.  相似文献   

19.
    
Forecasts from climate models and oceanographic observations indicate increasing deoxygenation in the global oceans and an elevated frequency and intensity of hypoxic events in the coastal zone, which have the potential to affect marine biodiversity and fisheries. Exposure to low dissolved oxygen (DO) conditions may have deleterious effects on early life stages in fishes. This study aims to identify thresholds to hypoxia while testing behavioral and physiological responses of two congeneric species of kelp forest fish to four DO levels, ranging from normoxic to hypoxic (8.7, 6.0, 4.1, and 2.2 mg O2/L). Behavioral tests identified changes in exploratory behavior and turning bias (lateralization), whereas physiological tests focused on determining changes in hypoxia tolerance (pCrit), ventilation rates, and metabolic rates, with impacts on the resulting capacity for aerobic activity. Our findings indicated that copper rockfish (Sebastes caurinus) and blue rockfish (Sebastes mystinus) express sensitivity to hypoxia; however, the strength of the response differed between species. Copper rockfish exhibited reduced absolute lateralization and increased escape time at the lowest DO levels, whereas behavioral metrics for blue rockfish did not vary with oxygen level. Both species exhibited decreases in aerobic scope (as a function of reduced maximum metabolic rate) and increases in ventilation rates to compensate for decreasing oxygen levels. Blue rockfish had a lower pCrit and stronger acclimation response compared to copper rockfish. The differences expressed by each species suggest that acclimatization to changing ocean conditions may vary, even among related species that recruit to the same kelp forest habitat, leading to winners and losers under future ocean conditions. Exposure to hypoxia can decrease individual physiological fitness through metabolic and aerobic depression and changes to anti‐predator behavior, with implications for the outcome of ecological interactions and the management of fish stocks in the face of climate change.  相似文献   

20.
    
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